Many electronic apparatuses represented by a computer or the like have an electronic component and a wiring substrate on which the electronic component is mounted. With a higher frequency of recent electronic apparatuses, there is a case where electromagnetic noise which is generated from a high-frequency circuit electromagnetically interferes with other electronic circuits in an electronic apparatus, and affects the operation of the electronic apparatus. As means for suppressing the electromagnetic interference, a structure in which a ground via is arranged in the outer circumference of a wiring substrate, thereby preventing leakage of electromagnetic noise from the end portion of the wiring substrate is suggested. In Patent Document 1 (Japanese Laid-Open Patent Application No. 7-263871), through holes are arranged densely in the periphery of a substrate, and conductor layers on the front and rear surfaces are connected together through the through holes. This technique is also described in Patent Documents 2 and 3.
As means for suppressing electromagnetic interference of a wiring substrate, Non-Patent Documents 1 and 2 suggest a structure in which an electromagnetic band gap (EBG) structure is applied. An EBG material refers to a structure in which a dielectric, metal, or the like is arranged periodically in a two-dimensional or three-dimensional manner to form a band gap for suppressing propagation of an electromagnetic wave in a specific frequency band inside the structure or on a plane.